Method of preparing bis (3-dialkylphosphonopropyl) esters



Sneak r F PREPARING BIS(3-DIALKY'L PHOSPHONOPROPYL) ESTERS Daniel Swern,Philadelphia, and Hogan B. Knight, Ainbler, Pa., assignors to the UnitedStates of America as represented by the Secretary of Agriculture NoDrawing. Filed Apr. 18, 1960, Ser. No. 23,105

7 Claims. (Cl. 260-461) 3 V :(GWFP. Ti e-1 S: Code 5 2 6 Anon-exclusive, irrevocable, royalty-free license in the invention hereindescribed, throughout the world for all purposes-of the United States.Government, with the power to grant sublicenses for such purposes, ishereby granted to the Governmentof the United States of America. :fjThisinvention relates to bis (3-dialkylphosphonoalkyl pounds of thegeneralFormula I OR Organic compounds containing two phosphorus atoms "BStQISTOf organic acids, and to process for their'prepar'a- H tion. Moreparticularly this invention relates to'cominthe molecule have ,heretofore been very diflicultto pre- ""parel' An object of the present inventionis to provide a P c h r y c mpau con ni WQ'P Q P atoms are'read'ilyobtained in good yields. r

An e o je t a t th s ntion i tqprepare a novel group ofcompounds'inwhichpolar groups are distributed throughout the molecule. A further objectis toprepare compounds containing two-phosphorus atoms per molecule foruse aswfire resistant, low-temperature plasticizers for polymers'such"as polyvinyl chloride-and for use as functional-fluids.

1' I 1 '11:; Other objects and advantages of the present invention willbecome apparent as the description thereof proceeds. According to thepresent invention the diphosphonate compounds of the general Formula I,wherein n is an integer from 0 to 8 and R is an alkyl radical, areprepared by the free radical addition of dialkyl phosphonates to diallylesters of aliphatic dibasic acids, as illustrated in the equation:

While the dialkyl phosphonate is exemplified with alkyl radicals such asmethyl, ethyl, n-butyl and 2-ethylhexyl, it is considered that thedialkyl phosphonate may contain any alkyl group and that the alklygroups may be different instead of identical as in present examples.

A molar excess of the dialkyl phosphonate is recommended for optimumyields and maximum rates of reaction. Since the excess phosphonate canbe recovered by vacuum distillation at the end of the reaction andreused, the general practice in preparing the present compounds has beento add several times the molar equivalent of phosphonate needed for thereaction.

Diallyl esters of the general formula wherein n is an integer from 0 to8 were prepared by conventional esterification procedures or bypurification of commercial esters. In the examples of diallyl esters ofoxalic, malonic, succinic, adipic, azelaic and sebacic zoate (0.0075'mole) were placed in a 200 m1. roundat n e t me. 2. 901.

acids illustrate the practical range of saturated dibasic acids,although diallyl esters of dibasic acids with longer carbon. chains. mayalso be employed to prepare other homologs. j

The'free radical addition of the phosphonate with the allyl ester ispreferably initiated by the use of a peroxide such as t-butylperbenzoate or benzoyl peroxide or ambisisobutyronitrile with moderateheating of the reaction mixture. The preferred initiator in terms ofyield "and shortness of reaction time ist-butyl perbenzoate. A-reactiontemperature of about C. is. a convenient selection in the range oftemperatures which may be employed with peroxides. 'When' thetemperature is too low the initiator may not decompose at a practicablerate; there-. action will be slow and take an undue amount of time toobtain a practical yield. If the temperature is too high the initiatormay: decompose too rapidly.

tained with the preferred peroxide initiator. The reaction is carriedout under a layer of inert gas such as nitrogen to prevent the undueformation ofsi'de products, especially-compounds which would interferewith the desired reaction.

A typical procedure for preparing the compounds of th s invention is asfollows: Preparatian o f bisi3-dialkylphosphonopropyl) esters 1 Dialkyl'phosphonate (0.90 mole) and t-buty-l erben bottom.3.-necked flaskequipped with a magnetic stirrer, a nitrogen inlet tube, dropping funneland thermometer. The contents of the flask Were heated to 100 C., withstirring, and diallyl ester (0.15 mole) was added dropwise at a slowrate while the temperature was maintained at about 100 to C. Additionalt-butyl perbenzoate (0.0075 mole) was added after 2 hours and 4 hours ofelapsed reaction time. (Total t-butyl perbenzoate added was 2.5 molepercent of the dialkyl phosphonate.) The addition of diallyl ester wascomplete after about 5 hours and the solution was stirred for anadditional 1% hours at the same temperature. The reaction mixture wasdegassed at l or less mercury pressure to remove the excess phosphonateand other volatiles and then molecularly distilled. (It should be notedthat the residue after removal of excess dialkyl phosphonate isessentially the desired product.) The main, constant boiling fractionwas collected and weighed. Yields were calculated from this weightsothat the values listed do not represent all the product.

Phosphorus analyses, infrared spectra and molecular refraction data wereobtained to confirm structure and to characterize the compounds.

Compounds prepared, yields, and some of the properties are presented inTable I.

The chemical composition of the compounds of this invention imparts fireresistant properties, and in addition to their use as low temperatureplasticizers, they are important for use as functional fluids andlubricant additives.

Possible variations to the present general class of compounds are theuse of aryl radicals instead of alkyl radicals on the phosphonates; theuse of other unsaturated diesters, such as divinyl, dimethallyl ordicrotyl esters of the dibasic acids; and the use of unsaturated oraromatic dibasic acids, such as maleataes or phthalates. Some of theseunsaturated esters yield compounds containing three phosphorus atoms.

TABLE I Bis(3-dialkylphonopropyl)esters of the general formula RO-P-ORRO-.P-0R J. 1 O 0 BIS (ii-DIE THYLPHOBPHONDPRQPYMESTERS R=--0,H.

Example n= Ester Yield, -B.P., 1m" 115 percent C./mm.- 16

0 31. 5 150/0. 003 .1. 4542 1.1075 1 77. 3 150/0. 004 1. 4517 1. 1833 267. 7 160/0009 1. 4548 1. 1802 4 04. 9 160/0. 007 1.4530 1.1475 7 59. 1170/0. 000 1. 4546 1.1171 8 Sebacate. '69.'2 HO/0.1000 1.4538 1. I047BIS(3-DIBUTYLPHOSPHONOPROPYL)ESEEBS R=-CH 0 Oxalate 50.8 160/0. 006 1.4524 1.0942 1 Malonate. 43. 8 17010.007 1.4536 1.0917 2 Sueciuate. 47. 6180/0. 007 1. 4526 1. 0831 '4 Adipate 6856 ISO/0.007 l. 4544 1.0698 763. 5 21010.013 1.4552 1.0515 8 :6 2. 0/ 010 1..4545 1. 0448 30BIB(3-DI-2-ETHYLHEXYLPHOSPHONOPROPYL) ESTERS CH3GHCH2CH2CH1OHZ HQOHSThese products were not distilled.

We claim: 1. A process for the preparation ofbis(3-dialkylphosphonopropyl) esters of the general formula wherein n isan integer from 0 to 8 and R is an alkyl radical comprising thefreeiradical addition of a dialkyl phosphonate to a diallyl ester of asaturated aliphatic dibasic acid having 2 to 10 carbon atoms.

2. The process of claim 1 in which the free radical additon of a dialkylphosphonate is initiated by adding t-butyl perbenzoate and heating themixture to about C.

3. The process of claim 1 wherein n is 8 and R is an ethyl radical.

4. The process of claim 1 wherein n is 7 and'R is a butyl radical.

5. The process of claim 1 wherein n is 4 and R is a butyl radical.

6. The process-of claim l wherein n is 4 and R is a 2-ethyl hexylradical.

7. The process of claim .1 wherein n is 2 and R is a butyl radical.

References Cited in the file of this patent UNITED STATES PATENTS2,710,301 Morris et a1. June 7, 1955

1. A PROCESS FOR THE PREPARATION OF BIS(3-DIALKYLPHOSPHONOPROPYL) ESTERSOF THE GENERAL FORMULA